The present invention relates to an RDS compatible receiver and an RDS data receiving method.
An RDS (Radio Data System) has been put into practical use, which allows a program name and a program type to be automatically received, and allows automatic search for an alternative station broadcasting the same program when a reception condition is poor, by adding additional data other than broadcast waves in FM broadcast programs.
RDS data is repeatedly broadcasted on a group basis in which each group is 104-bit data. Each group consists of four blocks, and each block is composed of a 16-bit information word and a 10-bit appended word. An appended word is generated by an exclusive OR operation between a check word derived by syndrome calculation of error correcting code from an information word and an offset word for block identification.
The check word is added to protect data from an error of received data caused by an effect of multipath noise or the like during reception of broadcast waves, and is based on shortened cyclic code.
Offset words added to four blocks in an RDS data group are “A”, “B”, “C” (or “C′”), “D” in order, and a sequential number of block data can be determined from an offset word.
A synchronization detecting circuit of an RDS receiver captures 26-bit data at first, and shifts it bit by bit until offset word matching is detected by syndrome calculation. If offset word matching is detected, next 26 bits are captured and offset word matching detection is performed thereon. Then, at a time when this block and its previous block are confirmed to match an offset sequence pattern, they are determined to be in a block synchronous state.
However, in such a synchronization determining method, if offset word matching detection in a first block is false positive due to an effect of a poor reception condition caused by multipath interference or the like, the blocks are found to be not synchronized when further 26 bits are captured and offset word matching detection is performed thereon. In this case, bit-by-bit shifting is again performed until offset word matching is detected. Thus, there is a problem that a long time is required until synchronization determination is completed.
To solve this problem, an RDS receiver has been proposed which performs determination of matching is performed each time one bit data is captured even after a first offset word matching detection is performed by syndrome calculation (For example, see Japanese Patent Laid-Open No. 8-256135). Therefore, even if a first offset word matching detection is false positive, a quick return to normal data capturing is allowed, and synchronization determination can be quickly performed.
However, an RDS receiver as described above needs syndrome calculation processing when offset word matching detection is performed, and its processing load is heavy. In addition, when a reception state is poor such as in a weak electric field, received data often contains an error, and synchronization establishment (detection) takes a long time.